1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices, and more specifically to a method of manufacturing semiconductor light emitting devices such as electroluminescent devices. The electroluminescent device which is a representative semiconductor light emitting device with which the present invention is concerned, can be used for a variety of display devices such as displays for computer terminal equipment and electronic typewriters, as well as monitoring devices for TV's.
2. Description of the Related Arts
The electroluminescent device which has heretofore been known can be represented by an alternating current thin film electroluminescent (ACTFEL) device. The ACTFEL device usually consists of a light emitting layer (e.g., thin ZnS:Mn film) held by an insulating layer on a glass substrate that supports one of the two opposing electrodes. The light emitting layer has heretofore been formed by sputtering or electron beam deposition. In either case, however, there is not obtained the light emitting layer that exhibits light emitting characteristics to a sufficient degree. That is, the layer after it is formed must be subjected to the heat treatment at 450.degree. C. or higher for about two hours. At the current technical level, furthermore, the device having the light emitting layer obtained by the above method exhibits an average intensity of about 20 ft-L even when it is excited with a voltage of as high as 200 volts at 60 Hz. If the thickness of the layer is reduced to decrease the exciting voltage, the intensity decreases, too, making it difficult to obtain satisfactory characteristics.
U.S. Pat. No. 4,496,610 and Japanese Patent Laid-Open No. 176897/1983 disclose a method of producing a light emitting layer composed of zinc chalcogenide doped with manganese by acting dimethyl zinc which is alkyl zinc and a gaseous hydrogenate compound of either sulfur or selenium which is chalcogen on a hot substrate in the presence of a tricarbonyl methylcyclopentadienyl manganese (TCM) vapor. According to this method, zinc chalcogenide is chemically grown by chemical vapor deposition (CVD) on the substrate and, at the same time, manganese which is a dopant is diffused. By adjusting the vapor pressures for forming the CVD atmosphere, therefore, there can be formed the light emitting layer that is stoichiometrically controlled. Furthermore, the light emitting layers having uniform quality and uniform thickness can be simultaneously formed on many substrates having large areas.
However, the light emitting efficiency of the light emitting layer obtained by this method is inferior to that of the light emitting layer obtained by the conventional sputtering method or electron beam deposition method. This is due to the fact that the TCM is poorly decomposed by heat. That is, the TCM can be sufficiently decomposed only when it is heated at a temperature of as high as 550.degree. C. or more. Moreover, oxygen exists in the chemical structure of TCM. According to this fabrication method, the light emitting thin film is crystallized most desirably at a temperature of from 300.degree. to 380.degree. C. When the layer is formed by CVD on the substrate heated in this temperature range, however, the TCM is not completely decomposed. Instead, intermediate decomposition products having an Mn-O-CO.sub.2 type coupling structure are formed in the light emitting layer, which are detrimental to obtaining light emitting layer of high crystallinity. Moreover, ZnO:Mn which works as a non-emitting center is formed in the crystal lattices. Further, when the layer is formed at a substrate temperature of higher than 400.degree. C., the reaction does not take place on the surface of the substrate but, instead, a so-called premature reaction takes place abruptly in an atmosphere on the surface of the substrate. Therefore, growth of crystals is impaired on the surface of the substrate, and satisfactory light emitting characteristics are not obtained.
Therefore, the manganese-doped zinc chalcogenide that exhibits satisfactory light emitting characteristics was not obtained by the above-mentioned prior art method.